Regulation of gene expression is fundamental to living processes such as growth control and development, and improved knowledge of the general transcription machinery is essential to understanding gene regulation. We have identified an RNA polymerase II holoenzyme in yeast which appears to be the form of RNA polymerase II that initiates transcription in vivo. This holoenzyme contains RNA polymerase II, general transcription factors, and a multiprotein complex composed of SRB, SWI and SNF proteins. The SRB/SWI/SNF complex is associated with the RNA polymerase II large subunit C-terminal domain (CTD) and has roles in the response to transcriptional activators and repressors. A similar holoenzyme was recently identified in mammalian cells. The experiments described in this proposal are designed to investigate the roles of RNA polymerase II holoenzyme components in control of class II gene expression using a combination of genetic and biochemical approaches in yeast. To accomplish this goal, the four specific aims of this proposal are: 1) to identify all of the CTD- associated components of the yeast RNA polymerase II holoenzyme; 2) to survey the yeast genome to identify the set of promoters that require SRB/SWI/SNF function in vivo; 3) to investigate further the subunit structure and function of the SRB/SWI/SNF subcomplex, and 4) to investigate how positive and negative regulators interact with the regulate SRB/SWI/SNF components of the holoenzyme. The health relatedness of this project derives from its contribution to the understanding of basic molecular mechanisms that control gene expression.